Two candles, same wax, same 10% fragrance load, and the same half percent of one woody ingredient. One label says H412 with no pictogram. The other says H411 with the dead tree and fish. The difference is a single number on the fragrance's safety data sheet: the M-factor. Here's what it is, where the formula comes from and how to check it on your own SDS.

The aquatic summation method

A candle is a mixture, and nobody tests a finished candle on fish and algae. So CLP classifies its long-term aquatic hazard with the summation method in Annex I, section 4.1.3.5.5.4. You take the percentage of each classified ingredient in the finished candle and run four checks in order, stopping at the first one that reaches 25%:

  • Chronic 1 (H410): (Chronic 1 × M) ≥ 25%.
  • Chronic 2 (H411): (M × 10 × Chronic 1) + Chronic 2 ≥ 25%.
  • Chronic 3 (H412): (M × 100 × Chronic 1) + (10 × Chronic 2) + Chronic 3 ≥ 25%.
  • Chronic 4 (H413): Chronic 1 + Chronic 2 + Chronic 3 + Chronic 4 ≥ 25%.

"Chronic 1" in each formula means the summed percentage of all ingredients classified Aquatic Chronic 1, and so on. Two things stand out. Each step down the ladder, the more toxic categories count ten times more, so a Chronic 1 ingredient weighs 100 times as much as a Chronic 3 one in the H412 check. And every Chronic 1 ingredient is also multiplied by its own M.

As we covered in candle hazard pictograms: H317, H411 and H412, the result matters for the label: H410 and H411 bring the environment pictogram, while H412 is a hazard statement with no pictogram and no signal word.

What an M-factor is

The M-factor ("multiplying factor") exists because some substances are toxic to aquatic life at tiny concentrations. Treating them like any other Chronic 1 ingredient would underestimate a mixture. CLP Table 4.1.3 sets the M from the substance's long-term toxicity (its NOEC) and whether it breaks down quickly in the environment. For a substance that isn't rapidly degradable:

  • NOEC above 0.01 and up to 0.1 mg/l: M = 1.
  • Above 0.001 and up to 0.01 mg/l: M = 10.
  • Above 0.0001 and up to 0.001 mg/l: M = 100, and so on in factors of ten.

Rapidly degradable substances get one step lower M for the same toxicity. There's a matching table for short-term (acute) toxicity. M-factors only exist for Aquatic Acute 1 and Aquatic Chronic 1 substances. The rule also changes what counts as "present": CLP says a Chronic 1 ingredient has to be taken into account from 0.1/M %, so from 0.01% in the candle when M is 10.

Where the M comes from

If a substance has a harmonised entry in CLP Annex VI with an M-factor, that value is binding. If Annex VI classifies it Aquatic Chronic 1 but gives no M, Article 10 says the manufacturer or importer must set one from the available data. Either way, since the 2020 update to the SDS rules, Section 3 of the safety data sheet must state the M-factor when one is available.

So what do common fragrance ingredients carry? We checked ECHA's Classification & Labelling Inventory on 29 September 2026:

  • d-Limonene (EC 227-813-5): harmonised Aquatic Acute 1 with an M-factor of 1, and Aquatic Chronic 3. It's one of the few fragrance materials with a harmonised M at all. More on it in limonene in citrus candles.
  • Galaxolide (HHCB, EC 214-946-9) and musk ketone (EC 201-328-9): harmonised Aquatic Acute 1 and Aquatic Chronic 1, with no M-factor in Annex VI. The supplier has to set it.
  • Dipentene (racemic limonene, EC 205-341-0): harmonised Aquatic Chronic 1, again with no harmonised M.
  • Tonalide (AHTN), alpha-pinene and methyl cedryl ketone: no harmonised aquatic entry, but industry self-classifies them Aquatic Chronic 1, and the notifications that state an M give M = 1.

In other words, M = 10 is uncommon among the materials in a typical candle fragrance. That's exactly why it catches people out when it does turn up: if a supplier's own data puts a 10 in Section 3, most makers never look at that column.

A worked example at 10% load

Take a hypothetical woody fragrance oil containing 30% d-limonene (Chronic 3) and one ingredient classified Aquatic Chronic 1. At a 10% load, the candle holds 3% limonene. Limonene alone adds just 3 to the H412 sum, nowhere near 25. The Chronic 1 ingredient decides everything.

Case 1: the oil has 2% of it, so the candle has 0.2%.

  • With M = 1: the H412 check is (1 × 100 × 0.2) + 3 = 23. Under 25, so the candle has no aquatic classification.
  • With M = 10: the H411 check is 10 × 10 × 0.2 = 20, under 25. The H412 check is (10 × 100 × 0.2) + 3 = 203. The candle is H412.

Case 2: the oil has 5% of it, so the candle has 0.5%.

  • With M = 1: H411 check 10 × 0.5 = 5, no. H412 check 100 × 0.5 + 3 = 53, yes. The candle is H412, no pictogram.
  • With M = 10: H410 check 10 × 0.5 = 5, no. H411 check 10 × 10 × 0.5 = 50, yes. The candle is H411 with the environment pictogram.

Same oil, same load, same 0.5%, and the M-factor alone adds a pictogram. For a single Chronic 1 ingredient in the finished candle, the thresholds shift by a factor of ten with each step of M:

  • M = 1: H412 from 0.25%, H411 from 2.5%, H410 from 25%.
  • M = 10: H412 from 0.025%, H411 from 0.25%, H410 from 2.5%.
  • M = 100: H412 from 0.0025%, H411 from 0.025%, H410 from 0.25%.

The short-term (acute) hazard uses the same idea, with Acute 1 × M ≥ 25% for H400. At candle loads it rarely triggers, which is why H410, H411 and H412 are the aquatic lines you actually see on candles.

What to check on your SDS

  • Read the M-factor column in Section 3 for every ingredient marked Aquatic Acute 1 or Aquatic Chronic 1. If it's blank for a Chronic 1 ingredient, ask the supplier rather than assuming 1.
  • Don't lower the load by guesswork. With M = 10, dropping from 10% to 8% only helps if it takes the Chronic 1 ingredient below the 0.25% line.
  • Recalculate when you change supplier. The same substance can carry a different self-set M from a different manufacturer.

Molekule reads the composition and M-factors from your fragrance's safety data sheet, checks each substance against ECHA's live harmonised classifications and runs the full summation for your candle at the load you choose. Calculate your candle's aquatic classification in Molekule.